<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>title</title>

</head>
<body>
<input type="button" value="后退" id="btn"/>
<script src="common.js"></script>
<script>
  //后退
  my$("btn").onclick = function () {
    window.history.back();
  };
</script>

</body>
</html>